To Fritz Müller   14 May 1877

My dear Sir,

I wrote to you a few days ago to thank you about Pontederia,¹ & now I am going to ask you to add one more to the many kindnesses which you have done for me. I have made many observations on the waxy secretion on leaves which throw off water (e.g. cabbage, tropæolum) & I am now going to continue my observations.² Does any sensitive species of mimosa grow in your neighbourhood? If so will you observe whether the leafletes keep shut during long-continued warm rain. I find that the leaflets open if they are continuously syringed with water at a temperature of about 19^c but if the water is at a temperature of 33–35^c they keep shut for more than 2 hrs & probably longer. If the plant is continuously shaken so as to imitate wind the leaflets soon open. How is this with the native plants during a windy day? I find that some other plants, for instance Desmodium³ & Cassia, when syringed with water, place their leaves so that the drops fall quickly off; the position assumed differing somewhat from that in so called sleep. Would you be so kind as to observe whether any of your plants place their leaves during rain so as to shoot off the water; & if there are any such I should be very glad of a leaf or two to ascertain whether they are coated with a waxy secretion

There is another & very different subject, about which I intend to write & should be very glad of a little information. Are earth worms (Lumbricus) common in S. Brazil, & do they throw up on the surface of the ground numerous castings or vermicular masses such as we so commonly see in Europe? Are such castings found in the forests beneath the dead & withered leaves. I am sure I can trust to you kindness to forgive me for asking you so many questions⁴

my dear Sir | Yours sincerely | Charles Darwin